In order to achieve optimized operation in a spark ignition internal combustion engine, it is necessary to vary the ignition timing or ignition point in accordance with the engine speed and load. For this purpose it is known practice to enter predetermined characteristic diagram values (sometimes referred to as characteristic map input) in a characteristic diagram (or characteristic map) of an electronic engine timing device in accordance with the load and speed such that the characteristic diagram values can be read out for each actual ignition point.
It is also known in the art to operate the internal combustion engine in the higher load range close beneath the knock limit in order to optimize fuel efficiency and low pollutant emission levels. However, care must be taken to ensure that the knock limit is not exceeded, since the risk of damage to the engine is great if the knock limit is exceeded too frequently. Since knock primarily occurs under wide-open-throttle operating conditions, it is therefore a direct constraint on engine performance. Further, since the position of the knock limit varies depending upon existing engine operating parameters, in particular fuel grade, temperature and air pressure, it is the known practice to control or regulate knocking on a short-term basis.
In accordance with the short-term knock control practice described above, when knocking combustion or knocking events occur, the predetermined characteristic diagram value taken from the characteristic diagram is reset one step at a time by a control stroke in the direction of retarded ignition through a relatively large retard correction value to a second adjusted diagram value for the actual ignition point. In the subsequent absence of any further pinging or knocking events, the retarded value for the actual ignition point is advanced, one control stroke at a time back to the original predetermined characteristic diagram value.
This short-term control or regulation is therefore related to the level of the predetermined characteristic diagram value entered in the characteristic diagram of the timing device for a particular engine. When the operating parameters are unfavorable, in particular when the fuel quality is poor, the knock limit may be relatively remote from the predetermined characteristic diagram value or map input. In this case, the knock control must be carried out with stepwise control strokes of an appropriate size and within a wide control band width. This has a disadvantageous effect on the control stability, since a relatively high number of knocking combustions, with sometimes violent and audible detonations, must be tolerated during the knock control period. This has an adverse effect on passenger comfort since knock produces unpleasant noise due to the sometimes audible detonations. In addition, such a protracted series of knocking combustions adversely affects the engine and the operation of the motor vehicle.
In the known practice, the short-term knock control starts with certain control strokes upon reaching an operating point of a particular speed and load. Upon leaving this operating point and reaching another operating point, the predetermined characteristic diagram value obtained from the characteristic diagram usually also changes in correspondence with the new operating point. The short-term control must then also re-adapt to these new conditions. When the transition conditions are unfavorable, a reactively high number of knocking combustions with sometimes violent detonations must be tolerated until the short-term control has re-adapted to the new operating point in the best possible manner.
Another problem with short-term knock control is that the first retard correction value has a fixed magnitude and cannot be automatically altered to account for changing operational conditions. For example, in order to stabilize out of knocking events as quickly and reliably as possible, a relatively large regulating action with a relatively large retard correction value is desirable. However, this is disadvantageous in that after subsequent knocking events, this technique causes the internal combustion engine to operate well below the knock limit in an inferior operating range since a large retard adjustment of the ignition angle has been made. It is therefore highly desirable to be able to reduce the magnitude of the correction value once such a large magnitude correction is no longer required.
It is also known practice to enter a plurality of set characteristic diagrams and make them available as required. For example, a connector may be installed in the engine compartment to switch from a specific characteristic diagram allocated to running on supergrade fuel to a second preset characteristic diagram for use when running on regular fuel. Alternatively, a characteristic diagram switch-over may be carried out automatically if a high number of knocking events is experienced. This automatic switch-over may be carried out by a learning function associated with a microprocessor or computer control means of the knock control system. Examples of such learning systems are disclosed in U.S. Pat. No. 4,829,962 and published international patent application No. PCT/EP88/00523, now U.S. Pat. No. 5,076,235, the subject matter of which are incorporated by reference as background for components of knock control systems of the type described herein. However these switch-overs represent an overall change or resetting of the ignition point for the entire engine characteristic diagram. Also, as with the case above, a number of knocking combustions must be tolerated during the switch-over period and the knock control range or band width is wide when transitions are made thus giving an unfavorable effect on the control stability.
Accordingly, there is a definite need in the art for an improved knock regulation system and method which overcomes the problems and shortcomings of the prior art.